1. Field of the Invention
The present invention relates to a silicone resin composition that is useful as an encapsulating material for an optical semiconductor element, and an optical semiconductor device that uses the composition.
2. Description of the Prior Art
Recently, high-brightness LEDs that exhibit strong light intensity and generate a large amount of heat have become commercially available, and are now being widely used, not only as the BLU units within liquid crystal televisions and mobile phones, but also for general illumination. JP 2010-1335 A (Patent Document 1) discloses that by adding an epoxy-containing silicone to a phenyl-containing silicone resin to improve the adhesiveness, an encapsulating material having excellent heat resistance, light-resistant stability and weather resistance can be provided. Further, JP 2009-527622 A (Patent Document 2) discloses a silicone resin composition comprising a phenyl-containing resin and a linear phenyl-containing hydrogenoligoorganosiloxane which is useful for extending the life of an LED.
In an LED package, a structure known as a lead frame which is prepared by silver-plating a copper sheet is used. However, it is known that if an LED that has been encapsulated with a silicone is left to stand under conditions in which a sulfur content is generated, then if the gas permeability of the silicone is high, discoloration tends to occur at the silver surface, and silver sulfide is formed resulting in a blackening of the surface. Because it is known that blackening of the lead frame causes a reduction in the brightness of the LED, it is desirable that the encapsulating resin exhibits low gas permeability. However, although the silicone resins described above exhibit excellent light resistance, heat discoloration resistance and impact resistance, in the case of the resin of Patent Document 1, the epoxy groups exhibit poor heat resistance and light resistance, and therefore the resin tends to suffer from discoloration under high temperature or high-intensity light. Further, in combinations of a phenyl-containing resin and a linear phenyl-containing hydrogenoligoorganosiloxane such as that disclosed in Patent Document 2, the heat resistance and light resistance are inferior to those of a methyl-containing silicone resin, and improving the reliability has proven difficult.    Patent Document 1: JP 2010-001335 A    Patent Document 2: JP 2009-527622 A